This invention is related to testing devices primarily intended for testing semiconductor devices such as transistors, diodes, controlled rectifiers and triacs. Semiconductors of this type act generally as "switches", that is, they normally exhibit two states: a high impedance or "non-conducting" state, and a low impedance or "conducting" state. Devices for testing these semiconductors therefore normally test internal impedance to determine if the impedance is proper for the state the device is expected to exhibit.
Such devices often have detachable alligator connectors or probes to make electrical connections with the terminals of the semiconductors. A test voltage is applied across the semiconductor through the connectors or probes. Diodes can be connected with the positive polarity (higher voltage) to the anode and the negative (ground) to the cathode, in which case the diode should exhibit a low impedance or conducting state. Alternatively, the terminals can be reversed, with the anode connected to ground and the cathode to the positive voltage, in which case the diode should exhibit a high impedance. If the diode has a lower reverse impedance than is normally expected, "leakage" current will pass through the diode. SCRs and triacs normally exhibit a high impedance until a positive voltage is supplied to their gate terminal, in which case they exhibit a low impedance. Also, when the gate voltage is removed, these devices should remain in a low impedance state until the voltage across the device drops to nearly zero. If SCRs and triacs do not exhibit these characteristics, they are defective. Thus, a test device should be capable of testing for the characteristics discussed above.
Many semiconductor devices, including breakdown devices, are intended to operate at relatively high voltages (in excess of 200 volts d.c.). Testing for leakage at low voltages often gives misleading results, as the semiconductor may test satisfactorily at low voltage and yet exhibit excessive leakage when subjected to operational voltages. Portable test units employing batteries normally only test at low voltage.
It is an object of the present invention to provide a portable testing device which is capable of testing the semiconductors at both high and low voltage levels.
It is another object of the present invention to provide for the use of a conventional voltmeter in conjunction with the testing device in order to read exact voltages across the semiconductor.
A further objective of the present invention is to provide a semiconductor testing device that can also be used to test capacitors.
These and other objectives of the present invention will become apparent upon reading the detailed disclosure which follows: